The small sprouts, and the grass like cereal plant (which I can't identify 100%, but which does resemble Carex, not something you particularly want), are weeds because they're growing somewhere you don't want them. Remove them, your bonsai tree needs all the root room it can get, it will not appreciate having to share that tiny amount of soil with any other plants.
Take care when extracting the roots of the grass like plant - at that size, they will have spread through the soil a fair bit by now, but you do need to get the roots out, just do it as gently as possible so as not to disrupt the roots of the bonsai tree, making sure the soil is good and wet first.
In future, remove any germinated seedlings as soon as you notice them, while they're still very small.